This invention relates to decorative features (recessed bubbles) for carbonated beverage containers (e.g. bottles) made of a plastic and to methods and apparatus for producing such containers.
xe2x80x9cPlasticxe2x80x9d is a polymerizable material that can be bi-axially oriented, e.g. polyethylene terephthalate (PET), polypropylene (PP) and acrylonitrile (AN) suitable for use in containers for liquid under pressure e.g., carbonated beverages.
xe2x80x9cPETxe2x80x9d as used herein shall be construed as including all materials defined hereinbefore as xe2x80x9cPlasticxe2x80x9d.
xe2x80x9cBubblexe2x80x9d as used herein is a circular, decorative feature formed by a deformation of the wall, which includes a shoulder, of a plastic container which does not extend outwardly (relative to the axis of the container) from the exterior surface of the container even when the container contains a liquid under pressure e.g. a carbonated beverage and is exposed to industry defined test procedures for such containers including exposure to stresses resulting from pressure and elevated temperatures during filling, packaging, distribution, sale and the end user actions.
xe2x80x9cCircularxe2x80x9d as used herein with respect to bubbles shall be construed to include ovals, ellipses, teardrops and other rounded shapes as well as circular shapes.
xe2x80x9cContainerxe2x80x9d as used herein shall be construed to include plastic bottles.
xe2x80x9cFrustumxe2x80x9d as used herein shall be construed as a truncated hollow right circular cone in which the apex is replaced by a plane section parallel to the cone base and which has parallel inner and outer surfaces and shall be construed to include a hollow cylinder which has parallel inner and outer surfaces.
PET for carbonated beverage containers has been used for many years. Many different shapes have been and are used to establish distinction between various brands of products. Some of these are decorative features formed in the surface of the container including ribs and swirls. Such decorative features may project inwardly and/or outwardly from the exterior surface of the container.
Generally CO2 is used for carbonated soft drinks but other gases such as N2 are also used to pressurize a plastic container. When the filled containers are exposed to typical service conditions especially higher than room temperature conditions, the pressure within the container increases while the plastic softens. This leads to creep (the plastic flows and distorts the container shape). One of the disadvantages of prior art decorative designs is that the PET will creep when exposed to excessive pressures and temperatures and many of the features will become distorted or even obliterated due to this creep. The desired distinctive features, particularly recessed features are then lost.
One attempt at producing a circular decorative feature is illustrated by the dimple 1, shown in FIG. 1 in an unpressurized state. In FIG. 1 a container 2 defines a longitudinal axis 3 and a wall radius 4. This dimple tends to invert and/or distort upon pressurization to a form such as that shown dashed in FIG. 1. This invention can be avoided by providing a thickened wall in the region of the dimple. This is, however, an undesirable solution due to the significant increase in material costs resulting from the additional material used, particularly when there is a substantial plurality of such dimples forming a distinctive pattern on the bottle. Inversions of the dimple is particularly undesirable because of resulting handling problems, labeling problems and questions of aesthetic appearance.
An object of the present invention is to provide a plastic container having at least one stable bubble, in a wall thereof, which does not extend outwardly from that wall especially when the container is pressurized e.g., by a carbonated beverage.
A further object of the present invention is to provide a blow mold design for producing a blow molded plastic container having at least one stable bubble, in a wall thereof, which does not extend outwardly from that wall.
Another object of the present invention to provide a method of producing a plastic container having at least one stable bubble, in a wall thereof, which does not extend outwardly from that wall.
According to the invention there is provided a bubble 6 formed in a wall 7 of a plastic container, the wall 7 defining an interior 14 of the container and having an interior surface 8, an exterior surface 9 and a wall thickness 29, the container being suitable for containing a liquid under pressure and the bubble comprising an integral structure having a central dome 10 defining a convex outer surface 11 facing toward an adjacent portion of the exterior surface 9, an annular trough 18 connected with the central dome 10, an outer ring 22 of curved cross-section and a first frustum 16 or 20 interconnected with the trough 18 and one of the central dome 10 and the outer ring 22, the annular trough 18 having an annular concave surface facing the adjacent portion of the exterior surface 9 and the outer ring having an annular concave surface facing toward the interior 14 of the container, to join, integrally, the bubble to the container wall 7 surrounding the bubble, the bubble having a thickness about equal to the wall thickness 29.
Preferably, the other of the central dome 10 and the outer ring 22 is connected to the trough 18 by way of a second frustum 16.
Also according to the invention there is provided a plastic container suitable for containing a liquid under pressure, comprising at least one bubble 6, formed in a wall 7 of the plastic container, the wall 7 defining an interior 14 of the container and having an interior surface 8, an exterior surface 9 and a wall thickness 29, the bubble comprising an integral structure having a central dome 10 defining a convex outer surface 11 facing toward an adjacent portion of the exterior surface 9, an annular trough 18 connected with the central dome 10, an outer ring 22 of curved cross-section and a first frustum 16 or 20 interconnected with the trough 18 and one of the central dome 10 and the outer ring 22, the annular trough 18 having an annular concave surface facing the adjacent portion of the exterior surface 9 and the outer ring having an annular concave surface facing toward the interior 14 of the container, to join, integrally, the bubble to the container wall 7 surrounding the bubble, the bubble having a thickness about equal to the wall thickness 29.
Preferably, the other of the central dome 10 and the outer ring 22 is connected to the trough 18 by way of a second frustum 16.
In addition, the invention provides a blow mold for blow molding a plastic container for containing a liquid under pressure, comprising at least one bubble 6 formed in a wall 7 of the plastic container, the wall 7 defining an interior 14 of the container and having an interior surface 8, an exterior surface 9 and a wall thickness 29, the bubble comprising an integral structure having a central dome 10 defining a convex outer surface 11 facing toward an adjacent portion of the exterior surface 9, an annular trough 18 connected with the central dome 10, an outer ring 22 of curved cross-section and a first frustum 16 or 20 interconnected with the trough 18 and one of the central dome 10 and the outer ring 22, the annular trough 18 having an annular concave surface facing the adjacent portion of the exterior surface 9 and the outer ring having an annular concave surface facing toward the interior 14 of the container, to join, integrally, the bubble to the container wall 7 surrounding the bubble, the bubble having a thickness about equal to the wall thickness 29.
Preferably the other of the central dome 10 and the outer ring 22 is connected to the trough 18 by way of a second frustum 16. Also preferably the blow mold comprises a first annular projection 48 having an outer extremity 50 and adjacent side surfaces complimentary to the trough and first frustum 20. In addition annular projections having outer extremities and adjacent side surfaces are complimentary to the first and second frustums 20 and 16.
Further the invention provides a method of producing a bubble 6, in a plastic container suitable for containing pressurized liquids, which does not, in use, extend outwardly from the exterior surface of the container, comprises:
a) providing a blow mold 44 having an axis 46 and bubble forming features in the form of an annular projection extending toward the axis 46 of the mold cavity and container to be formed, the annular projection having an outer extremity and adjacent side surface complimentary to a trough 18 or 66 and a frustum 16, 20;
b) pre-heating a preform to facilitate blow molding to form the container and the bubble;
c) introducing the preform into the blow mold;
d) applying a gas at a pressure sufficient to inflate and deform the preform into contact with the mold cavity to form the container and into contact with bubble forming features to produce the bubble at least one of a wall and shoulder of the container, the bubble being formed failing to contact the mold cavity in the region of a central dome 10 and a substantial portion of an outer ring 22 of the bubble;
e) cooling the container; and
f) removing the container with the bubble(s) formed therein from the blow mold cavity.